1. Things you need to know before you play the game
Blower Door Basics
Blower Door Basics -- SimBuilding.info
Things you need to know before you play the game

2. Air Leakage Affects Home Performance
We’ve already discussed how air leakage affects home performance. Air leakage is what the blower door measures.
Blower Door Basics ___ SimBuilding.Info
Photo courtesy of EnergyStar.gov

3. Air Leakage Requires: A hole. Pressure difference across that hole.
The bigger the hole or higher the pressure difference, the more airflow.
To reduce airflow, we can reduce the size of the hole or lower the pressure difference.
Holes in the air barrier wouldn’t matter without pressure differences.
Air leakage requires:
A hole.
Pressure difference across that hole. This can be caused by a number of factors, called driving pressures (e.g., temperature, wind).
The bigger the hole or higher the pressure difference, the higher the volume of air leakage.
To reduce airflow, reduce the size of the hole or lower the pressure difference. Holes and pressure differences usually go hand in hand.
The leakage we care about is usually between the inside and outside of the house. Air leakage within the conditioned space in a house is less important.
The bigger the temperature or pressure difference, the greater the air and heat flow. This is why measures that reduce heating demand are often more cost effective than those that reduce cooling demand. The temperature difference between inside and outside in a very cold climate in winter is two to three times the difference between inside and outside in even the hottest climate in summer.
Blower Door Basics ___ SimBuilding.Info
Graphic developed for the US DOE WAP Standardized Curricula
December 2012

4. Air Leakage: Temperature
T = Temperature Difference
Winter
Summer
70
10
90
70
Delta T (T) is the temperature difference.
Flow is from hot to cold.
T=60
T=20
Graphic developed for the US DOE WAP Standardized Curricula
Blower Door Basics ___ SimBuilding.Info
December 2012

5. P = Pressure Difference
Air Leakage: Pressure
P = Pressure Difference
Positive
Flow is from positive (high) to negative (low) pressure.
Negative
Blower Door Basics ___ SimBuilding.Info
Graphic developed for the US DOE WAP Standardized Curricula
December 2012

6. Measuring Pressure Difference
Pascal (metric standard)
1 Pascal = weight of one Post-It note
249 Pascals = 1 inch water column (American standard)
1” water column = pressure required to suck 1” of water up a straw
Units for measuring pressure difference:
Pascal is the metric standard and the standard in building science. Some HVAC technicians use the American standard, inches of water column.
1 Pa = approximately the weight of one Post-It note.
249 Pa = 1 inch of water column.
1” water column = pressure required to suck 1” of water up a straw.
Blower Door Basics ___ SimBuilding.Info
August 2010

7. Measuring Building Air Leakage
Natural driving forces
Blower Door
Pressure differences too small to measure reliably.
Exaggerates pressure differences so they can be measured reliably and the results are repeatable.
Natural driving forces – Pressure differences caused by natural driving forces of wind effect, stack effect, and combustion and ventilation are too small to measure reliably. These naturally occurring pressure differences change with the wind and temperature, and are not repeatable.
Blower door – This controlled driving force exaggerates pressure differences so they can be measured reliably and the results are repeatable. With this tool, we can measure leakage from a standard baseline.
We can convert the exaggerated air leakage measured with the blower door to air leakage that would occur under natural conditions.
Exaggerated air leakage measured with the blower door gives us an idea of the amount of air leakage that would occur under natural conditions.
Blower Door Basics ___ SimBuilding.Info
August 2010

8. Blower Door Testing
Blower door testing is used to quantify and locate air leakage by using a calibrated fan to depressurize a house.
Blower door testing locates and quantifies air leakage by using a calibrated fan to depressurize a house.
This photo is of a Minneapolis Blower Door manufactured by the Energy Conservatory in Minneapolis, MN.
Photo courtesy of NRCERT
Blower Door Basics ___ SimBuilding.Info
August 2010

9. Controlled Driving Force
Use a Blower Door as a Controlled Driving Force
Using the blower door depressurizes the house, drawing air through all the holes between inside and outside the house.
Negative pressure
Using the blower door depressurizes the house, drawing air through all the holes between inside and outside the house.
Using the blower door as a driving force, air is sucked out of the house faster than it can be replaced. This creates a measurable pressure difference in order to perform diagnostics.
This is different from how the house behaves under normal conditions. Normally, air would be infiltrating through some of the holes and exfiltrating through others. With the blower door running, the home is depressurized so air infiltrates all the holes except the door where the fan is set up.
Blower Door
Blower Door Basics ___ SimBuilding.Info
Graphic developed for the US DOE WAP Standardized Curricula
December 2012

10. Units for Measuring Airflow
Cubic Feet per Minute (CFM)
Rate of airflow.
Based on the size of a home and the number of occupants, a home should have a certain amount of fresh air when the home is closed up.
CFM50 (standard for blower door)
Blower door measures the rate of airflow in CFM when the pressure difference between the inside of the house with reference to outside is -50 Pascals.
Cubic feet per minute.
Rate of airflow – A cubic foot of air is about the amount in a basketball. When we measure CFMs, we're determining how many basketballs per minute leak into and out of the home.
The minimum ventilation requirement (MVR) is the amount of fresh air a home requires when it is closed up to maintain healthy indoor air quality based on the size of the home and the number of occupants. MVR is the target number of CFMs not to go below when air sealing the home.
CFM50 (standard for blower door).
A blower door measures the rate of airflow in CFM when the pressure inside of the house is -50 Pa with reference to outside. The exaggerated pressure difference is reliably measurable and repeatable.
Blower Door Basics ___ SimBuilding.Info
August 2010

11. Approximate Leakage Area
25”
20”
Divide CFM50 by 10
For example: 5,000 CFM50/10 = 500 in.2
Calculating the approximate leakage area is a good way to think about the overall leakiness of the home and to express that leakiness to clients.
Divide CFM50 by 10 to determine approximate square inches of holes in the home.
5,000 CFM50/10 = 500 square inches.
This simple equation indicates that starting with the equivalent of a 500-square-inch hole, air sealing reduced the size of the hole to only 150 square inches.
Q: If the pre-air-sealing reading were 5,000 CFM50, what post-air-sealing blower- door reading would indicate a reduction of 350 square inches of leakage area?
A: 1,500 CFM50.
Photo courtesy of NRCERT
Blower Door Basics ___ SimBuilding.Info
August 2010

12. Summary
The blower door is a controlled driving force used to quantify air leakage.
Air leakage is measured in cubic feet per minute at a pressure difference of 50 pascals with reference to another space.
Blower door readings can be converted to air leakage under natural conditions, total size of opening, and more.
The blower door is a controlled driving force used to quantify air leakage.
Air leakage is measured in cubic feet per minute at a pressure difference of 50 pascals with reference to another space.
Minimum ventilation requirements assure adequate fresh air.
Air changes per hour relate air leakage to building size.
Blower door readings can be converted to air leakage under natural conditions, total size of opening, and ACH.
Blower Door Basics ___ SimBuilding.Info
August 2010